The present invention concerns a drive train for a motor vehicle, which includes a coupling device between a drive unit and a transmission, in which the coupling device has at least one coupling arrangement which can be activated by a pressure medium, and in which coupling arrangement, the pressure medium is provided by a pump arrangement.
Coupling systems are described, for example, in DE 100 56 954 A1 and DE 101 02 874 A1, and reference to the disclosed content thereof is expressly made in the description of the invention which appears below.
The coupling system is especially configured as a wet clutch double coupling system with two multiple disk clutch coupling arrangements, which can be activated in a hydraulic manner by slave cylinders integrated into the coupling device. Double coupling systems of this type are described, for example, in DE 100 04 179 A1.
Wet clutch double coupling systems, for the activation of the multiple disk clutch couplings, require a low flow rate of the pressure medium under high pressure. For cooling the friction pads and/or disks, they require a comparatively high flow rate of the operating medium, under comparatively low pressure. By comparison with conventional solutions that include a pump that is mechanically driven by the drive unit and that constantly provides a flow rate or output pressure corresponding to the rotational frequency of the drive unit at any given moment, the technique of using an independently adjusted pump arrangement for each flow rate is known, for example, in the aforementioned DE 100 56 954 A1 and DE 101 02 874 A1 documents.
In the case of pumps that are driven by an electrical motor, however, it has been shown that, with drive units characterized by especially high performance ratings and/or especially high rotational frequencies, the requirement of the coupling device for cooling oil can be so high that the use of an electrical motor to drive an electrical motor pump to cool the coupling device becomes inconvenient, as a result of the excessively large amount of room required for a pump of the desired performance rating. For energy-related reasons, however, returning to the conventional solution, which involves a pump that is permanently driven by the drive unit, cannot be envisioned. It is known from prior art that, even in the case of a pump that is permanently driven by the drive unit, it is possible to provide a way of controlling and/or adjusting the output pressure and/or the output flow rate of the pump, without requiring too great a degree of mechanical and control-related effort and expense.